- previously introduced `getOrDefault` as a dictionary _get_ method,
  now complete the transition and use it everywhere instead of
  `lookupOrDefault`. This avoids mixed usage of the two methods that
  are identical in behaviour, makes for shorter names, and promotes
  the distinction between "lookup" access (ie, return a token stream,
  locate and return an entry) and "get" access (ie, the above with
  conversion to concrete types such as scalar, label etc).

Update of overRhoPimpleDyMFoam and overInterDyMFoam solvers.
Adding corresponding tutorials with best possible settings
The main effort was put on reducing pressure spikes as the
stencil change with hole cells on the background mesh.

- in many cases can just use lookupOrDefault("key", bool) instead of
  lookupOrDefault<bool> or lookupOrDefault<Switch> since reading a
  bool from an Istream uses the Switch(Istream&) anyhow

STYLE: relocated Switch string names into file-local scope

Adds overset discretisation to selected physics:
- diffusion : overLaplacianDyMFoam
- incompressible steady : overSimpleFoam
- incompressible transient : overPimpleDyMFoam
- compressible transient: overRhoPimpleDyMFoam
- two-phase VOF: overInterDyMFoam

The overset method chosen is a parallel, fully implicit implementation
whereby the interpolation (from donor to acceptor) is inserted as an
adapted discretisation on the donor cells, such that the resulting matrix
can be solved using the standard linear solvers.

Above solvers come with a set of tutorials, showing how to create and set-up
simple simulations from scratch.

XiDyMFoam               : compressible version of XiFoam
oscillatingCylinder     : 2D case with cylinder moving up and down
annularCombustorTurbine : part of 3D combuster using cyclicPeriodicAMI